ABSTRACT Asthmatic human airway smooth muscle (HASM) differs from normal HASM in at least three ways - dysregu- lated contraction, myocyte hypertrophy, and abnormal chemokine elaboration - but the mechanisms that un- derlie these asthmatic HASM phenotypes remain poorly understood. We have discovered that the HLA-G - LILRB - SHP signaling pathway, which is known to regulate immune system responses, also operates in HASM. Importantly, signaling through this pathway promotes each of the asthmatic HASM characteristics listed above. The major objective of this proposal is to analyze the inflammatory and genetic regulation of this path- way in HASM in order to identify novel strategies that prevent or reverse these asthmatic HASM phenotypes. In preliminary studies, we found that LILRB1, LILRB2, and their family member LILRB4, and SHP2 (but not SHP1) are all expressed in human ASM; that LILRB receptors activate SHP2 within human airway myocytes; and that SHP2 increases the force of contraction and elasticity, stimulates Akt signaling and hypertrophy, and activates NFB and chemokine elaboration. Thus, the HLA-G - LILRB - SHP2 signaling pathway is intact in HASM, and its activation imparts asthma-like phenotypes to airway muscle. Furthermore, the HLA-G - LILRB - SHP2 axis may be abnormally exaggerated in asthma because: soluble HLA-G is three times more abundant in BAL fluid of asthmatic subjects than normal volunteers; several immunomodulatory molecules found in asthmatic airways can increase LILRB expression; and genetic variations in each component of this pathway (HLA-G, LILRB1, LILRB2, LILRB4, and PTPN11, which encodes SHP2) are associated with asthma and/or bronchial hyperresponsiveness. Together, these data suggest the novel and biologically plausible hypotheses that overactive HLA-G - LILRB - SHP2 signaling imparts an asthmatic HASM phenotype, and that therapeutic intervention to interfere with this signaling pathway might ameliorate ASM abnormality in asthma. To test these hypotheses, we propose to: 1) determine how selected immunomodulatory molecules influence HLA-G - LILRB - SHP2 signaling in normal and asthmatic HASM; 2) evaluate how genetic variations in LILRB1, LILRB2, or LILRB4 that are associated with BHR or asthma influence HLA-G - LILRB - SHP2 signaling in normal or asthmatic HASM; and 3) delineate the molecular mechanisms by which altered SHP2 signaling causes normal HASM to acquire an asthmatic HASM phenotype. These studies will reveal how HLA-G - LILRB - SHP2 signaling regulates ASM function; which genetic and inflammatory mechanisms modulate that regulatory role; and whether inhibition of this pathway can prevent or reverse acquisition of the asthmatic HASM phenotype.